In the present case, “lines” should be taken to mean all flow paths for fluid media. Consequently, these include not only flexible hoses or rigid lines but also channels, flow chambers or even just through openings machined into bodies.
Coating systems of this kind are used to coat objects such as vehicle bodies or body components with the aid of electrostatically operating application devices, for example in the automotive industry. In this context, the coating material, e.g. a paint, is discharged by the application device and subjected to an electric field, in which the coating material discharged is ionized and transferred by virtue of electrostatic forces to the object, which, for this purpose, is at ground potential, for example. An application device of this kind can, for example, be a high-speed rotary atomizer with a rotating bell-shaped plate, from which extremely small paint droplets are thrown, thus forming a paint mist.
In electrostatically operating systems, the lines must build up an insulating section in a direction away from the application device during the coating process, and must be clean and dry to achieve this. In such cases, the lines are manufactured from an electrically insulating material.
In the delivery of paints and other liquid materials through lines, the pigging technique has become established, in which technique a sliding body, referred to as a “pig”, pushes a volume of material ahead of it. During this process, the pig is subjected to a pressurized fluid on the side facing away from the delivery volume, it being possible, for example, for said fluid to be compressed air or even a cleaning fluid, which cleans the line behind the pig.
In general, there are “ring lines” as material sources for the coating material, wherein a fluid connection between a ring line carrying material and the piggable supply line can be established by means of the supply unit. Before the pig then forces the material in the direction of the application device, the material is first of all forced into the system by the inherent pressure prevailing in the material sources, i.e. the ring lines.
The line section leading to the application device is quite long and can have a relatively small diameter, e.g. approximately 1 mm, at least in some segments. Owing to this relatively small diameter, there is a pressure loss along the line, making delivery of the material merely by the inherent pressure of the connected material source more difficult. Moreover, the inherent pressure in the material sources is generally not constant but is subject to technically related, irregular fluctuations, which also makes reproducibility of the delivered volume more difficult.